1. Field of the Invention
The present invention relates generally to power supply devices and more particularly to a novel switching power supply apparatus having its energy storage component in the primary circuit of the output transformer rather than in the secondary circuits.
2. Description of the Prior Art
Although multiple output regulated power supplies have been available for many years, all such devices have suffered from disadvantages that from operational and efficiency standpoints must be overcome. For example, those supplies which utilize commonly driven but separate pulse-width modulated converters suffer the disadvantages that they are expensive, technically complex and not highly reliable; those devices which utilize a single pulse-width modulated converter having multiple secondaries have the disadvantages that auxiliary outputs have poor load regulation, a minimum load is required on the primary output and no auxiliary remote sensing is possible; those devices which utilize a single pulse-width modulated converter having multiple transformer secondaries with pass regulators, or which use multiple transformers with pass control in their primaries suffer from loss of efficiency and have minimum load requirements on the primary output; and those devices which utilize a front end chopper with a squarewave converter require an additional switching transistor, impose large stresses on the converter transistors, have poor auxiliary load regulation, have slow transient response and have low efficiency.
A more detailed description of these prior art approaches and their advantages and disadvantages may be found in an article entitled "Which Multiple Output Technique Should Your Switching Supply Use" by Walter J. Hirschberg, published in EDN, Mar. 5, 1978, pages 91-95.